because your ipod is going to stop working when iOS 5 is released?Not a relevant argument to a third gen iPod touch user.
I don't know if I believe this rumor, the 3GS still has essentially the same hardware as the iPhone 4 so I see no reason it won't run the latest OS, maybe have some features stripped, but as long as it's not as bad as iOS 4 on the 3G was I think Apple is making a mistake if they don't release it.